const panels = document.querySelectorAll('.panel');

function toggleOpen() {
    this
        .classList
        .toggle('open');
}

// function toggleActive(e) {
//     if (e.propertyName.includes('flex')) {
//         this
//             .classList
//             .toggle('open-active');
//     }
// }

panels.forEach(panel => panel.addEventListener('click', toggleOpen));
// panels.forEach(panel => panel.addEventListener('transitionend', toggleActive));